Question

All electrons ejected from a surface by an incident light of wavelength 200 mm, can be stopped before travelling 1 m in the direction of a uniform electric field of 4N/C. What is the work function of the surface?

Answer 1

From photoelectric law:

$V_0=\frac{hc}{e}(\frac{1}{\lambda }-\frac{1}{{\lambda }_0})-\left(1\right)V_0=E\times d=4\times 1=4Vfrom\left(1\right):V_{0}e=\frac{hc}{\lambda }-\frac{hc}{{\lambda }_0}\to \frac{hc}{{\lambda }_0}=W=\frac{hc}{\lambda }-V_{0}e=6.39\times {10}^{-19}J=4eV$